The 26-foot-long, nine-feet-tall skeleton represents Colorado’s State Dinosaur and appears in the museum alongside the frame of an Allosaurus. It weighed up to 10 tonnes when it roamed the area now knows as Colorado 150 million years ago, and its remains were eventually found in 1936 by a class of high school students, taught by Frederick Carl Kessler, who would go on to help professional palaeontologists in excavating the fossil.

Mike Triebold, President of Triebold Paleontology, wanted to add the famous Kessler Stegosaurus to his catalogue of casts, and the new Royal Gorge Dinosaur Experience (RGDE) in Canon City also wanted to feature it. The grandfather of RGDE owner, Zach Reynolds, would regularly join Kessler on dinosaur digs from the 1940s through the 60s, and so RGDE wanted a copy of the Stegosaurus that was discovered just a few miles down the road and had family and community ties.

TPI, with the approval of the museum, got to work. The team had to negotiate the sheer size of the skeleton, but also the fact that the carcase was mounted on its exhibit with no forethought of it needing to be removed when it was installed in the 1990s. Steel was shaped around the skeleton, welded in place and permanently puttied to the bones. Moulding in silicone was pretty much impossible, but scanning in three dimensions wasn’t.

Using the Artec Spider 3D scanner and the Artec Studio processing software, TPI was able to scan individual bones and regions of the skeleton and upload them as individual projects in Artec Studio. By the end of the scanning process, the team had 629 individual scans across 71 individual scan projects sitting inside the Artec Studio software. Those numbers would have been even higher, but a decision was made to skip scanning bones that could instead be mirror imaged, like the arms, legs and ribs. Once scanned and uploaded to Artec Studio, the data was aligned, cropped, and converted to 3D mesh files. TPI says the alignment features within Artec Studio were paramount to the success of the project.

“We needed to three-dimensionally digitise the skeleton that could not be dismantled so that a replica could be 3D printed,” said Matt Christopher, TPI. “The dimensions and surface details needed to be close enough to what we would get from a silicone mould so that we could hand-finish 3D prints to look exactly like the original specimen.

“Aligning each scan was as simple as manually orienting to a loose approximation of the correct position and letting the alignment tool refine the fit to perfection. Using Artec Studio to create and control the mesh generated from the aligned scans allowed us to extract the exact level of detail we wanted for manipulating and 3D printing.”

Another feature enjoyed by the TPI team was Studio’s filtering capabilities which removes all elements smaller than the master scan, freeing all exported meshes of artefacts. Small holes were also automatically filled using the software’s hole-filling algorithm. These meshes were imported into ZBrush, where articulated elements were separated, surfaces that couldn’t be reached with the 3D scanner were reconstructed and steel armature that obscured some of the bone surfaces were removed.

“Had we been scanning individual, unmounted bones, it would have been easy to generate complete, watertight meshes directly out of Artec Studio that would have required no additional post processing,” Christopher explained. “With the steel armature remaining to be removed and the obstructed surfaces left to be reconstructed, watertight meshes were not really an option or a necessity for remaking the Stegosaurus.”

Then, the scan files needed to be 3D printed, and TPI combined the capabilities of small desktop printers, like the Formlabs Form 2 SLA machine, and larger-format options, like the Atlas platform from Titan Robotics. In all, printing of the entire skeleton took around six months. Once the scan data was printed, they were resurfaced by hand and prepared for moulding by adding mock-ups for internal steel armature, and some areas of the skeleton were outlined as sections which should be moulded collectively rather than individually. Each bone or assembly, typically called masters, were then moulded in silicone rubber using high quality liquid silicone rubbers in two-part to multiple-part moulds, a technique TPI staff have been doing for close to 30 years. Once moulding was completed, the moulds were fitted with internal steel before plastic resins would be implemented in the casting process. Here, plastic is poured around the steel, meaning no external armature is needed. With the casts poured around the armature, the skeleton can now be assembled in a variety of poses and the steel protruding from inside each plastic cast can be welded together.

The resulting model of the Kessler Stegosaurus will be on permanent display at the RGDE in Canon City, Colorado. TPI is now considering deploying the same method to reproduce the Allosaurus skeleton that accompanies the Kessler Stegosaurus at the Denver Museum of Nature & Science.